The field of the invention is apparatus and methods for sensing, or producing a signal analogous to, a temperature associated with fluid within a conduit. More particularly, the invention is concerned with the production of a signal which is analogous to the mean temperature of combustion products flowing in a turbo machine.
Turbo machines including combustion turbine engines such as turboshaft, turboprop and various kinds of jet engines are frequently rated, controlled and safeguarded by reference to a temperature of the working fluid flowing within the machine. In the specific case of turboshaft, turboprop and jet engines, it is common to sense the temperature of combustion products flowing from a combustor of the machine in order to assess the operating condition of the engine. However, experience has shown that the combustion products are not isothermal. In a nominal engine of a particular kind, the combustion products will display a considerable temperature variation or transverse temperature profile downstream of the combustor. Further, among serially produced like engines having an annular flow path for the combustion products, there will exist a considerable circumferential temperature variation in the combustion products under identical operating conditions. The reasons for such transverse and circumferential temperature variations are legion. Among these reasons are variations of the fuel and air distributions within particular combustors, differences due to tolerences in component parts of an engine, varying dispositions and relationships of fit of the associating components of an engine, and many other factors. Despite the variables affecting the temperature profiles of combustion products in serially produced engines, all the engines of a series will be rated and operated to the same nominal design or mean temperature of combustion products. Consequently, it is common to employ a multitude of thermocouples arrayed both circumferentially and transversely to sense the temperature of the combustion products at a multitude of discreet points. From the multitude of temperatures indicated by the thermocouples an average temperature is derived for use as a reference in operating and safeguarding an engine. Despite such measures, it is not uncommon for properly operating engines to be removed from service because the average temperature indicated by an array of thermocouples has erroneously indicated an overtemperature condition. Similarly, it sometimes happens that a true overtemperature condition will elude an array of thermocouples so that an engine is damaged in use.
Accordingly, it is recognized in the turbomachine art that an array of thermocouples, while providing an indication of average temperature of combustion products at discreet points, does not fulfill the requirement for measurement of mean temperature of working fluid within an engine. Further, it is recognized that such an average temperature is, at best, an approximation based on incomplete data, although it does provide some information about the operation of the engine by comparison to nominal design values. Reliance upon such approximated information is unsettling and vexatious to both designers and operators of turbo engines.